A continuously variable valve lift system for actuating a combustion valve of an engine includes a camshaft having a camshaft lobe rotatable about an camshaft axis of rotation. A rocker assembly is pivotable for providing reciprocating motion to the combustion valve. A control shaft is rotatable about a control shaft axis of rotation such that rotation of the control shaft about the control shaft axis of rotation changes the position of the rocker assembly to vary the lift of the combustion valve. An actuator selectively rotates the control shaft between a minimum lift position and a maximum lift position. A bias spring surrounding the control shaft axis of rotation biases the control shaft only from the minimum lift position to a predetermined position which is intermediate the minimum lift position and the maximum lift position upon failure of the actuator.
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1. A continuously variable valve lift system for actuating a combustion valve of an internal combustion engine, said continuously variable valve lift system comprising:
an engine camshaft having an engine camshaft lobe, said engine camshaft lobe being rotatable about an engine camshaft axis of rotation;
a rocker assembly that is pivotable for providing reciprocating motion to said combustion valve, said rocker assembly having a rocker assembly input member for receiving motion from said engine camshaft lobe and a rocker assembly output member for transmitting motion to said combustion valve;
a control shaft rotatable about a control shaft axis of rotation, wherein rotation of said control shaft about said control shaft axis of rotation changes the position of said rocker assembly, thereby varying the lift of said combustion valve;
an actuator for selectively rotating said control shaft between a minimum lift position and a maximum lift position;
and a bias spring surrounding said control shaft axis of rotation for biasing said control shaft only from said minimum lift position to a predetermined position which is intermediate said minimum lift position and said maximum lift position upon failure of said actuator.
2. A continuously variable valve lift system as in
3. A continuously variable valve lift system as in
4. A continuously variable valve lift system as in
5. A continuously variable valve lift system as in
6. A continuously variable valve lift system as in
7. A continuously variable valve lift system as in
8. A continuously variable valve lift system as in
9. A continuously variable valve lift system as in
10. A continuously variable valve lift system as in
11. A continuously variable valve lift system as in
12. A continuously variable valve lift system as in
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This patent application claims the benefit of U.S. provisional patent application Ser. No. 61/554,550 filed Nov. 2, 2011, the disclosure of which is hereby incorporated by reference in its entirety.
The present invention relates to a continuously variable valve lift system for varying the lift of a combustion valve in an internal combustion engine; more particularly to a continuously variable valve lift system with a mechanism for providing a default lift of the combustion valve.
Internal combustion engine manufacturers have been developing continuously variable valve lift (CVVL) systems to actuate combustion valves (intake valves and/or exhaust valves) of an internal combustion engine in an effort to increase fuel economy, decrease emissions, and otherwise improve the performance of the internal combustion engine. These CVVL systems may be applied to only the intake valves, to only the exhaust valves, or to both the intake valves and the exhaust valves depending on the need of the internal combustion engine. CVVL systems are used to vary the magnitude of lift of the combustion valves where valve lift is commonly understood to be the distance the combustion valve is moved from its valve seat. One CVVL system is shown in United States Patent Application Publication No. US 2011/0061618 which is commonly assigned and is incorporated herein by reference in its entirety. In this CVVL system, an engine camshaft with an engine camshaft lobe is rotated about an engine camshaft axis as is customary in the internal combustion engine art. A rocker assembly receives input from the engine camshaft lobe via a roller on the rocker assembly where rotational motion of the engine camshaft lobe causes the rocker assembly to pivot in a reciprocating manner. An output portion of the rocker assembly acts on a roller of a finger follower which pivots on a hydraulic lash adjuster. When the finger follower pivots about the hydraulic lash adjuster, a combustion valve is opened and closed. In order to vary the valve lift of the combustion valve, a control shaft is provided which is rotatable about a control shaft axis by an actuator. Rotation of the control shaft about the control shaft axis changes the position of the rocker assembly which results in a change of valve lift of the combustion valve. In the event of a failure of the actuator, it may be desirable for the CVVL system to default to a predetermined valve lift which allows the internal combustion engine to start and to run satisfactorily until a repair can be made.
U.S. Pat. No. 7,886,703 teaches a CVVL system with a default mechanism for providing a default valve lift in the event of a failure of the actuator which is an electric motor. In this arrangement, rotary motion of the electric motor is converted into linear motion by a ball screw. The linear motion created by the ball screw is converted into rotational motion of the control shaft by linkage attached to the ball screw and the control shaft. The default mechanism includes two compression springs which act in opposing directions to provide a default valve lift. One drawback to this default mechanism arrangement is that the actuator must work against at least one of the compression springs over the full range of motion of the control shaft during operation which increases the capacity requirements of the actuator. Another drawback to this default mechanism is that it must be used in a system where rotational motion of the actuator is converted into linear motion.
U.S. Pat. No. 7,418,933 teaches a CVVL system with a default mechanism for providing a default valve lift in the event of a failure of the actuator which is an electric motor. In this arrangement, the electric motor has an output shaft with a driving gear which meshes with a driven gear. The driven gear is connected to a shaft of a worm gear which meshes with a sector gear of the control shaft of the CVVL system. The default mechanism includes a large diameter gear and a small diameter gear which move with the shaft of the worm gear. A first default spring surrounds the control shaft to bias the control shaft from a maximum lift position to a default position intermediate the maximum lift position and a minimum lift position. A second default spring acts on a gear set, which includes a large diameter gear and a small diameter gear, to bias the control shaft from the minimum lift position the default position. One drawback to this default mechanism arrangement is that the actuator must work against at least one of the default springs over the entire range of motion of the control shaft during operation which increases the capacity requirements of the actuator. Another drawback to this default mechanism is the cost and complexity that are added by the gears that are needed only for the second default spring to bias the control shaft from the minimum lift position to the default position.
What is needed is a CVVL system with a default mechanism which minimizes the size requirements of an actuator of the CVVL system. What is also needed is a CVVL system with a default mechanism that adds minimal components and complexity to the CVVL system.
Briefly described, a continuously variable valve lift system is provided for actuating a combustion valve of an internal combustion engine. The continuously variable valve lift system includes an engine camshaft having an engine camshaft lobe rotatable about an engine camshaft axis of rotation. The continuously variable valve lift system also includes a rocker assembly that is pivotable for providing reciprocating motion to the combustion valve. The rocker assembly includes a rocker assembly input member for receiving motion from the engine camshaft lobe and a rocker assembly output member for transmitting motion to the combustion valve. The continuously variable valve lift system also includes a control shaft rotatable about a control shaft axis of rotation such that rotation of the control shaft about the control shaft axis of rotation changes the position of the rocker assembly, thereby varying the lift of the combustion valve. The continuously variable valve lift system also includes an actuator for selectively rotating the control shaft between a minimum lift position and a maximum lift position. The continuously variable valve lift system also includes a bias spring surrounding the control shaft axis of rotation for biasing the control shaft only from the minimum lift position to a predetermined position which is intermediate the minimum lift position and the maximum lift position upon failure of the actuator.
This invention will be further described with reference to the accompanying drawings in which:
In
Control shaft 16 is eccentrically fixed to control shaft disc 30 such that control shaft disc 30 rotates eccentrically about control shaft axis of rotation 17 when control shaft 16 is rotated. High engine load events as shown in
When control shaft disc 30 is in the high engine load mode, as shown in
Referring now to
It will be observed that displacement (i.e. rotation) of control shaft 16 from the position shown
Reference will now be made to
A default mechanism, shown in part as bias spring 76, is provided in order to move control shaft 16 to a predetermined position intermediate of the minimum lift position and the maximum lift position in the event of a failure of electric motor 60. Bias spring 76 is a torsional spring which surrounds control shaft axis of rotation 17. Bias spring stationary end 78 of bias spring 76 is grounded to internal combustion engine 14 while bias spring moveable end 80 of bias spring 76 applies a biasing force to driven gear 70 only from the minimum lift position to the predetermined position. Driven gear 70 includes cutaway sector 82 which provides reaction surface 84 for bias spring moveable end 80 to act upon from the minimum lift position to the predetermined position. In an alternative not shown, an arcuate slot may be substituted for cutaway sector 82. When control shaft 16 reaches the predetermined position, bias spring moveable end 80 is prevented from moving further by spring stop 86 which is fixed to internal combustion engine 14.
While bias spring 76 will urge control shaft 16 to the predetermined position if electric motor 60 fails when control shaft 16 is positioned between the minimum lift position and the predetermined position, bias spring 76 does not urge control shaft 16 to the predetermined position if electric motor 60 fails when control shaft 16 is positioned between the maximum lift position and the predetermined position. Instead only the forces generated by engine camshaft lobe 22 and combustion valve 12 acting on rocker assembly 36 will urge control shaft 16 to the predetermined position. When control shaft 16 reaches the predetermined position, reaction surface 84 will come into contact with bias spring moveable end 80. Bias spring 76 is selected to provide a spring force that will resist the forces generated by engine camshaft lobe 22 and combustion valve 12 acting on rocker assembly 36. As a result, the forces generated by engine camshaft lobe 22 acting on rocker assembly 36 are unable to wind up bias spring 76 and control shaft 16 is maintained at the predetermined position.
Since electric motor 60 only needs to work against one bias spring for only a portion of the total range of motion of control shaft 16, electric motor 60 does not need to be increased in load capacity to overcome the forces of two springs which would be needed if a bias spring were provided to bias control shaft 16 toward the predetermined position from both the minimum lift position and the maximum lift position. Furthermore, since there is only one bias spring, there are fewer CVVL system components and the design of the CVVL system is simplified and more compact.
While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited.
Patent | Priority | Assignee | Title |
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